As marine-ice around Antarctica retracts, a vast ‘blue carbon’ sink, in the form of living biomass, is emerging. Properly protected and promoted Antarctic blue carbon will form the world’s largest natural negative feedback on climate change. However, fulfilling this promise may be challenging, given the uniqueness of the region and the legal systems that govern it. In this interdisciplinary study, we explain: the global significance of Antarctic blue carbon to international carbon mitigation efforts; the urgent need for international legal protections for areas where it is emerging; and the hurdles that need to be overcome to realize those goals. In order to progress conservation efforts past political blockages we recommend the development of an inter-instrument governance framework that quantifies the sequestration value of Antarctic blue carbon for attribution to states’ climate mitigation commitments under the 2015 Paris Agreement. Key policy insights Blue-carbon emergence around Antarctica’s coastlines will potentially store up to 160,000,000 tonnes of carbon annually. Blue-carbon will emerge in areas of rich biomass that will make it vulnerable to harvesting and other human activities; it is essential to incentivise conserving, rather than commercial exploitation of newly ice-free areas of the Southern Ocean. Antarctic blue carbon is a practical and prime candidate to build a cooperative, inter-instrument, non-market mitigation around; this should be considered at the ‘blue COP’ UN Climate change discussions in Spain. Allowing Antarctic fishing states to account for the carbon storage value of blue carbon zones through a non-market approach under the Paris Agreement could provide a vital incentive to their protection under the Antarctic Treaty System. The Scientific Committee on Antarctic Research would be the ideal body to facilitate the necessary connections between the relevant climate and Antarctic governance regimes.